Polyperoxides are used in industry for cross linking polymers. Among the polyperoxides which have been used in cross linking polymers is .alpha., .alpha.'-bis(t-butylperoxy) diisopropylbenzene. The .alpha., .alpha.'-bis(t-butylperoxy) diisopropylbenzene has been available as a blend of the meta and para isomers where the ratio of meta to para isomers is about 2.0/1 and where the meta isomer constitutes about 68% of the blend and the para isomer constitutes about 32% of the blend. This blend, available from Hercules Incorporated, Wilmington, Del. as Vul-Cup.RTM. organic peroxide, is produced by a process as disclosed in U.S. Pat. No. 3,658,914 incorporated herein in its entirety, using di-isopropyl benzene as a starting material.
Generally, the isomer ratio of the polyperoxide is determined by the process of alkylating cumene. This process results in a meta to para isomer ratio of about 2:1.
Also, .alpha., .alpha.'-bis(t-butylperoxy) diisopropylbenzene is available either in its pure meta or para form.
While these blends are useful in the cross linking of polymers, the temperature range over which these materials melt sometimes interferes with absorption of the liquid peroxide into the polymers. If the .alpha., .alpha.'-bis(t-butylperoxy) diisopropylbenzene melts near the softening point of a polymer to be cross linked, problems frequently arise due to polymer particles sticking together during the absorption process. This is a problem with the available 2/1 blend as well as with nearly pure meta or para isomers.
It has been discovered that by selecting certain ratios of the meta and para isomers in the polyperoxide, polyperoxides having lower melt point ranges may be obtained. These polyperoxides may be produced either through selecting the desired ratio of di-isopropyl benzene as a starting material if that material is to be oxidized to its corresponding diol form or selecting di-isopropyl benzene diol with the desired isomeric ratio or through blending of meta and para isomers of the polyperoxide.
A need exists for peroxides which melt at a lower temperature than the polyperoxides described hereinabove. U.S. Pat. No. 4,450,302 discloses peroxide blends that have low melting points and which are useful in the crosslinking of polymers such as polyethylene, EPDM and copolymers of ethylene and vinyl acetate. However, these peroxide blends exhibit high volatility and poor scorch resistance. Scorch is known in the art as premature crosslinking of a polymer system prior to forming the polymer into desirable shapes. Poor scorch resistance of the peroxide blends of U.S. Pat. No. 4,450,302 is as a result of these peroxide blends containing dicumyl peroxide which has a scorch initiation temperature approximately 10.degree. C. below the scorch initiation temperature of the inventive peroxides blends and polyperoxides.
The peroxide blends of U.S. Pat. No. 4,450,302 discloses high amounts of t-butyl cumyl peroxide. T-butyl cumyl peroxide is a relatively volatile material and has a vapor pressure of 20 mm Hg at ambient temperature. The vapor pressure of the .alpha., .alpha.'-bis(t-butylperoxy) diisopropylbenzene is essentially 0 mm Hg at ambient temperature. It is desirable to minimize the volatility of peroxides used in crosslinking polymers because peroxide loss from polymer/peroxide blends effects the manner in which the polymer cures.